Fuel cells based on proton exchange membrane technology are typically assembled by laminating together a large number of individual cells. Each cell comprises a membrane-electrode assembly (MEA) with associated anode and cathode plates on either side of the MEA. Gaskets are used to ensure a fluid-tight seal around the MEA.
A typical layout of a conventional fuel cell 10 is shown in FIG. 1 which, for clarity, illustrates the various layers in exploded form. A solid polymer ion transfer membrane 11 is sandwiched between an anode 12 and a cathode 13. Typically, the anode 12 and the cathode 13 are both formed from an electrically conductive, porous material such as porous carbon, to which small particles of platinum and/or other precious metal catalyst are bonded. The anode 12 and cathode 13 are often bonded directly to the respective adjacent surfaces of the membrane 11. This combination is commonly referred to collectively as the membrane-electrode assembly.
Sandwiching the polymer membrane 11 and porous electrode layers 12, 13 is an anode fluid flow field plate 14 and a cathode fluid flow field plate 15. Intermediate backing layers 12a, 13a, also referred to as diffuser or gas diffusion layers, may also be employed between the anode fluid flow field plate 14 and the anode 12 and similarly between the cathode fluid flow field plate 15 and the cathode 13. The backing layers 12a, 13a are porous to allow diffusion of gas to and from the anode and cathode surfaces as well as assisting in the management of water vapour and liquid water in the cell.
The fluid flow field plates, or electrode plates, 14, 15 are formed from an electrically conductive, non-porous material by which electrical contact can be made to the respective anode electrode 12 or cathode electrode 13. At the same time, the fluid flow field plates facilitate the delivery and/or exhaust of fluid fuel, oxidant and/or reaction product to or from the porous electrodes 12, 13. This is conventionally effected by forming fluid flow passages in a surface of the fluid flow field plates, such as grooves or channels 16 in the surface presented to the porous electrodes 12, 13.
The electrode plates 14, 15 are electrically insulated from each other and the flow fields across the plates 14, 15 are kept fluid tight using gaskets that are positioned around the fluid field areas between the fluid flow plates and the polymer membrane 11.
To allow useful amounts of power to be generated, individual cells such as that shown in FIG. 1 need to be assembled into larger stacks of cells. This can be done by laminating multiple cells in a planar stack, resulting in alternating anode and cathode plate connections. Connecting individual cells in series allows for a higher voltage to be generated by the stack, and connecting cells or groups of cells in parallel allows for a higher current to be generated. Multiple stacks may be used to generate electrical power, for example for use in an electrical power unit for a hydrogen-powered vehicle.
Large numbers of cells need to be assembled to form each individual stack. Manufacturing such stacks therefore requires many separate steps, each of which requires accurate positioning of the various layers making up each cell. Any misalignment can result in failure of the entire stack, for example by an electrical short-circuit or through leakage from fuel or oxidant paths. It is therefore important for the application of fuel cell technology to mass production that a manufacturing process for assembling the stack is fast, accurate and reliable.
A particular problem with assembly of such fuel cell stacks relates to the accurate positioning and alignment of components such as gaskets, which by their nature are flexible and therefore more difficult to align with respect to other less flexible components such as the metallic fluid flow field plates, particularly when sub-millimeter location accuracy is required. Gaskets may be supplied in the form of die cut sheets of adhesive gasket material, which will require removal from a backing paper before being positioned in place on a substrate, for example on a fluid flow field plate or an MEA.
Accurately positioning such adhesive materials is difficult to achieve by hand without the aid of alignment tools, and is highly labour intensive.
The use of pre-cut sheets for the flexible components of the fuel cell assembly is also problematic because the sheets may be subject to movement and distortion during handling and assembly. The use of a backing paper, for example with adhesive layers such as gaskets, will tend to reduce distortion but may be insufficient to maintain repeatable sub-millimeter level accuracy of positioning of such gaskets.
A further problem is how to assemble a laminated fuel cell with as few operations as possible, to speed up the overall process and reduce the number of variables that may be subject to positioning tolerances.
A more general further problem is how to speed up the overall process of assembling a laminated fuel cell without sacrificing either accuracy or repeatability.
This disclosure and aspects of the embodiments herein address one or more of the above mentioned problems.